it would be nice if the iPad’s mic could be used as a talkback, but …. NOPE.
Most sound folks I have encountered use an old junky SM58 and plug it in to the talkback input with a short cable.
A gooseneck mic is nice because it is faster than picking up and holding a 58, and a talkback mic is going to sound cleaner simply because it is probably spoken into from a distance if used properly.